Open Process Control (OPC) is a software interface standard that allows WINDOWS programs run on computers to communicate with industrial hardware devices used in manufacturing plants and refineries. The acronym OPC comes from OLE (Object Linking and Embedding for Process Control). OLE is partially based on the WINDOWS component object model (COM) standard and OPC shares some common features with COM. OPC is implemented over a client/server network.
The OPC server contains a software program that converts the hardware communication protocols used by industrial hardware devices such as programmable logic controllers (PLC) into the OPC protocol. The OPC client software includes programs to connect to the industrial hardware devices such as a human-machine interface. The OPC client uses the OPC server to receive data and/or transmit commands to the industrial hardware devices.
The OPC client connects to one or more servers using a token. The token includes client credential information that is validated by the server to decide whether to allow or prevent access to the server. The proxy connection and the server are not always in the same domain so that the client's token credentials may not be understood which can result in a connection failure. In another case, the server may not support the specific token being used which also results in a connection failure.